Monday, 13 February 2012

Analogic / Digital converter

Analogic / Digital converter
This integrated circuit (AD 7821) allows to convert an analogic signal in a 8 bits value with a 1 µs conversion time, thus with a 1 MHz frequency. There are faster converters allowing to obtain a better resolution (10, 12, 14 or 16 bits).

Pin Assignments for AD7821
  1. Input
  2. Data bit 3
  3. Data bit 2
  4. Data bit 1
  5. Data bit 0
  6. WR/RDY
  7. Mode
  8. RD
  9. INT
  10. Ground
  11. Vref -
  12. Vref +
  13. CS
  14. Data bit 4
  15. Data bit 5
  16. Data bit 6
  17. Data bit 7
  18. OFL
  19. Vss
  20. +Vcc


Components List
Pot. : P1 = 20 kΩ
A/D Converter = AD7821
trigger inverter = 1/4 CD4093
The signal resulting from the amplifier is applied to the pin 1 (Input). The reference voltage is adjusted by means of P1. It is very summary but that works. We can also use a specific component to obtain this reference voltage (zener diode for ex.).
The pulse "start of conversion" results from the clock generator (having a 5 V level compatible with the converter) and the pulse "End of conversion" is sent to the PC interface, as well as 8 bits data. We can also send these data through buffer circuits (74245 by eg) to secure the exchanges interface-converter. The logic gate (1/4 CD4093) can be another inverter.

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